Field of the Invention
Embodiments relate to the in situ manufacturing of graphene-containing silicon carbide (SiC) ceramic composites.
Background of the Related Art
Graphene, a sp2 hybridized carbon sheet, possesses outstanding electronic and physico-chemical properties, and it is considered one of the strongest materials ever produced. Graphene sheets have been proposed for use as an ideal filler in the fabrication of robust polymer and ceramic composites. Graphene is commonly synthesized by chemical exfoliation of graphite-like materials. Some exfoliation methods are based on the intercalation of oxide species between the graphene layers of graphite. These result in graphene oxide monolayers (GO).
GO's subsequent reduction to graphene (rGO) can be achieved chemically or thermally. The main disadvantage of this method is the poor mechanical and conducting properties of rGO as compared to pristine mechanically exfoliated graphene. Alternative routes have also been explored for producing highly crystalline graphene, mainly used for the fabrication of electronic devices. These are the chemical vapour deposition (CVD) of hydrocarbons on metallic surfaces or the thermal decomposition of SiC that leads to the epitaxial growth of graphene (EG). Epitaxial growth typically occurs on 6H—SiC (0001) crystals after ultrahigh vacuum annealing at ˜1200° C. or at higher temperatures (>1500° C.) under a quasi atmospheric pressure of argon.
Yannopoulos, et al., have recently reported the fast generation of large-area and homogenous EG on SiC substrates using a CO2 laser as heating source. This method does not require high vacuum and operates at low temperatures with fast heating and cooling rates. Homogeneous graphene layers have also been epitaxially grown on SiC substrates by direct deposition of carbon.
SiC ceramics exhibit excellent thermal and high temperature mechanical properties suitable for a wide range of structural applications. The addition of graphene as filler further enhances those properties, including outstanding tribological and electrical performance. In this context, preliminary data on graphene/ceramic nanocomposites demonstrated outstanding improvements in the mechanical and electrical properties of alumina and silicon nitride by the introduction of graphene nanoplatelets (GNPs), reaching even better results than those obtained using carbon nanotubes.
The production of bulk graphene/ceramic nanocomposites is mainly done by mixing dispersions of graphene nanosheets or GNPs and ceramic powders in convenient solvents and subsequent densification at high temperatures. One challenge to the fabrication of homogenous graphene/SiC ceramic composites using this method is the dispersion of graphene into the ceramic matrix. An unsuccessful dispersion will lead to the formation of graphene agglomerates and defects in the composite. This causes a decrease in many beneficial properties of the material.
Another important problem is the manufacturing cost to produce large batches of monolayer or few layers graphene (FLG) needed to fill the ceramic matrix with contents up to 50% in weight. For instance, 100 mL of graphene oxide aqueous solution with 80% of carbon content can cost up to $740.00 in the current market.
A further challenge is the densification of the graphene/SiC powder compacts. SiC ceramics containing sintering additives require very high sintering temperatures for their densification (1600-2000° C.). This can lead to the graphene degradation, causing a deleterious effect on the properties of the material.
In summary, the manufacturing of bulk graphene/ceramic composites can present problems linked to graphene agglomeration, uncompleted composite densification or graphene degradation, especially for SiC-based materials where very high sintering temperatures are required. All these facts affect the properties of the composite.